1. Field of the Invention
The present invention relates to high density polyolefin and films, and to methods for producing such resins and films. In another aspect, the present invention relates to barrier grade resins and films wherein the films comprise at least one layer of a linear high density polyethylene (HDPE) having low permeability, and to methods for producing such barrier grade resins and films. In even another aspect the present invention relates to HDPE barrier grade films produced on a film line configured with a neck height of greater than about 15 inches, and to methods of producing films comprising at least one layer of such resins.
2. Description of the Related Art
Having been around since the early 1950""s, Ziegler-type polyolefin catalysts, their general methods of making, and subsequent use, are well known in the polymerization art. While much is known about Ziegler-type catalysts, there is a constant search for improvements in their polymer yield, catalyst life, catalyst activity, and in their ability to produce polyolefins having certain properties.
Polyolefins, for example polyethylene or polypropylene, have an extremely wide range of applications which include materials and containers in the form of films, sheets, or hollow articles. Tailoring the properties of polyolefins to fit a desired applicability is constantly ongoing.
When light passes through a sheet or film of polyolefin, scattering can cause the light to deviate from the incident direction. If the scattering is significant enough, it will cause a reduction in the transmitted light and the sample will appear to be hazy. This scattering can be from either surface imperfections which are generally related to low gloss, or from scattering bodies within the sample itself. In the case of polyethylene, the scattering bodies are from the regions of high crystalline polymer which increase as the polymer density increases. Increasing the polymer density is achieved by increasing both the size and quantity of crystalline lamella at the expense of the amorphous polyethylene. Therefore, it is normal to observe a decrease in the clarity of conventional polyethylene blown film as the density of the bulk polymer increases. Additionally, it is normal to observe a decrease in the gloss of the film as the density of the polymer increases.
U.S. Pat. No. 6,110,549, issued Aug. 29, 2000 to Hamiota et al., discloses a sealant resin composition for producing sealant film. The Hamiota resin comprises a high density polyethylene as the main component and a linear low density polyethylene polymerized by use of the metallocene catalyst.
U.S. Pat. No. 6,045,882 issued Apr. 4, 2000 to Sandwort, discloses a multilayer, biaxially stretched, flexible, thermoplastic film comprising at least two surface layers and a core layer disposed there between. Each of the two surface layers comprise a blend of a copolymer of ethylene and a C3-C10, xcex1-olefin, and a high density polyethylene.
U.S. Pat. No. 6,027,776 issued Feb. 22, 2000 to Mueller, discloses multilayer films for packaging and administering medical solutions wherein the films comprise improved optical properties. The Mueller films generally include: a) an interior layer of homogeneous ethylene/alpha-olefin copolymer; b) a first exterior layer of a material selected from the group consisting of homopolymer or copolymer of polypropylene, a blend of homopolymer or copolymer of polypropylene and elastomer, high density polyethylene, and copolyester; and c) a second exterior layer of a material selected from the group consisting of polyamide, copolyamide, polyester, copolyester, high density polyethylene, polypropylene, propylene/ethylene copolymer, and polycarbonate.
U.S. Pat. No. 5,852,152, issued Dec. 22, 1998 to Walton et al., discloses a biaxially oriented, heat-shrinkable film-making process and film with improved toughness and extrusion processability. The Walton film comprises a layer of at least one substantially linear ethylene homopolymer or interpolymer, wherein the substantially linear ethylene polymer essentially lacks a measurable xe2x80x9chigh densityxe2x80x9d fraction.
In spite of the advancements in the art, barrier grade films comprising at least one layer of a linear high density polyethylene (HDPE) barrier grade resin wherein the polyethylene comprises a narrow rheological breadth parameter, and a narrow molecular weight distribution have not been described.
Furthermore, methods of producing a barrier grade film comprising a layer of a HDPE barrier grade resin wherein the resin comprises a narrow rheological breadth parameter, and a narrow molecular weight, wherein the method comprises blowing a HDPE barrier grade film on a film line using a high stalk configuration have not been described.
Thus, there is a need in the art for films comprising a layer of a linear HDPE barrier grade resin wherein the resin comprises a density greater than about 0.955 g/cc, a narrow rheological breadth parameter of greater than about 0.22, a narrow molecular weight distribution (MWD) of less than about 7.0, and a water vapor transmission rate of less than about 0.60 g.mil/100 in2/day.
There is another need in the art for a method of producing a film comprising a layer a linear HDPE barrier grade resin wherein the resin comprises a density greater than about 0.955 g/cc, a narrow rheological breadth parameter of greater than about 0.22, a narrow molecular weight distribution (MWD) of less than about 7.0, and a water vapor transmission rate of less than about 0.60 g.mil/100 in2/day, wherein the resin is blown on a film line configured with a neck height of greater than about 15 inches.
These and other needs in the art will become apparent to those of skill in the art upon review of this specification, including its drawings and claims.
It is an object of the present invention to provide barrier grade films comprising a layer of a linear HDPE barrier grade resin wherein the resin comprises a density greater than about 0.955 g/cc, a rheological breadth parameter of greater than about 0.22, a molecular weight distribution (MWD) of less than about 7.0, and a water vapor transmission rate of less than about 0.60 g.mil/100 in2/day.
It is another object of the present invention to provide a method for producing barrier grade films comprising a layer of linear HDPE barrier grade resin wherein the HDPE comprises a density greater than about 0.955 g/cc, a rheological breadth parameter of greater than about 0.22, a molecular weight distribution (MWD) of less than about 7.0, and a water vapor transmission rate of less than about 0.60 g.mil/100 in2/day, wherein the resin is blown on a film line configured with a neck height of greater than about 15 inches.
One embodiment of the present invention is directed to a film comprising a layer of linear HDPE barrier grade resin. Generally the HDPE resin is a polyethylene homopolymer and has a water vapor transmission rate (WVTR) of less than about 0.60 g.mil/100 in2/day. In addition, the HDPE utilized in the films of the invention comprises a rheological breadth parameter xe2x80x9caxe2x80x9d of greater than about 0.22, and a narrow molecular weight distribution (MWD) of less than about 7.0.
Another embodiment of the invention is directed to a method for producing a film comprising a layer of HDPE barrier grade resin. The process generally comprises blowing a HDPE resin into a film, wherein the HDPE resin comprises a water vapor transmission rate (WVTR) of less than about 0.60 g.mil/100 in2/day, and the HDPE comprises a rheological breadth parameter xe2x80x9caxe2x80x9d of greater than about 0.22, and a narrow molecular weight distribution (MWD) of less than about 7.0. The films of the invention may be produced on any film line, such as, for example, an Alpine film line. Generally the films are blown on a film line configured with a neck height greater than about 15 inches. This is an innovative approach to making a barrier grade resin because conventional barrier grade resins are conventionally run in a no neck configuration.
These and other objects of the present invention will become apparent to those of skill in the art upon review of this specification, including its drawings and claims.